Re: Quantum Computers

Doug Jones (
Tue, 17 Aug 1999 10:46:23 -0700

John Clark wrote:

> In another book called "The Ghost In The Atom" Deutsch does give what
> he considers a definitive test of the Many World Interpretation and
> a Quantum Computer is part of it, but it must be intelligent.
> In the Deutsch test a conscious quantum computer shoots electrons
> at a metal plate that has 2 small slits in it. It does this one
> at a time. After leaving the plate the electrons hit some
> photographic film, but do not look at the photograph until
> later. The quantum mind has detectors near each slit so it
> knows which slit the various electrons went through.

There's your fallacy- detectors at the slits perturb the wave function of the electrons, and destroy the interference pattern. It's the detector, not whatever looks at the *output* of the detector, that matters. Erasing the recording of the output does not eliminate the interaction that the detector had with the electrons earlier.

The rest of the handwaving is pointless.

> The quantum mind now signs a document saying that it has observed
> each and every electron and knows what slit each electron went
> through.


> In the Copenhagen interpretation when the results of a
> measurement enters the consciousness of an observer the wave
> function collapses,

No, when the measurement is *made* by any brainless piece of machinery (via intereaction via photons or other particles), the wave function collapses. This can be demonstrated by placing a detector in a two-slit experiment, and not connecting the output to anything. The interference pattern goes away regardless.

> in effect all the universes except one disappear without a trace
> so you get no interference. In the many worlds model all the other
> worlds will converge back into one universe when the electrons hit
> the photographic film but their influence will still be felt,
> you'll see indications that the electron went through slot A only
> and indications that it went through slot B only, and that's
> what causes interference. Time will tell who's correct.

Nope- if a detector is placed on either slit, the interference pattern goes away. *Only* if there is no measurement made at either slit can an interference pattern occur. No mumbo jumbo, no half-dead cats.

Doug Jones, Freelance Rocket Plumber